Field of the Invention
The present invention relates to a restoration filter generation device and method for generating a restoration filter to be used in a restoration process, an image processing device and method for performing the restoration process using the restoration filter, an imaging device including the image processing device, and a non-transitory computer-readable medium for generating the restoration filter.
Description of the Related Art
In an image obtained by the imaging of a subject with an imaging device such as a digital camera, an image degradation deriving from various aberrations in an optical system (an image-taking lens and the like) sometimes appears. The image degradation by the aberrations can be expressed by a point-image distribution function (PSF: Point Spread Function) and the like. Therefore, by generating a restoration filter based on the degradation characteristic of the optical system such as the PSF and performing a point-image restoration process (restoration process) on the image data using the restoration filter, it is possible to reduce the image degradation.
Such a point-image restoration process is classified roughly into a frequency restoration process and a phase restoration process. The frequency restoration process equates the modulation transfer function (MTF) characteristic of the image degraded by the optical system. In the phase restoration process, a picture is moved depending on the frequency such that the asymmetric PSF form is restored to a point as much as possible.
On this occasion, the aberration in the optical system such as the image-taking lens differs depending on the wavelength, and therefore, it is desirable to perform the point-image restoration process using restoration filters that are different among the images for the respective colors of RGB. However, the process for each color results in a heavy computation load, and therefore, it has been considered to perform the point-image restoration process only on the luminance component, which has a great visual effect. In this case, since the PSF form for the luminance cannot be defined, it is necessary to consider some sort of criterion and find a middle ground so as not to generate an adverse effect on the restoration performance.
An image processing device described in Japanese Patent Application Laid-Open No. 2010-140442 (hereinafter referred to as PTL 1) calculates PSFs for the respective colors of RGB, synthesizes the PSFs for the respective colors with previously defined weighting coefficients for the respective colors to calculates a PSF for a luminance system image (also referred to as a luminance component image), and generates a restoration filter for the luminance system image based on the PSF. Then, the image processing device performs a point-image restoration process on the luminance system image, using the restoration filter, and thereafter, generates an RGB image based on the luminance system image after the restoration process and a color-difference system image (also referred to as a color component image) that is not a target of the point-image restoration process. Thereby, it is possible to reduce the image degradation such as false colors.